Self-oscillating constant frequency switching regulator with phase control of voltage regulation loop

ABSTRACT

A self-oscillating switching mode regulator is frequency regulated by controlling the phase of the voltage control feedback signal. The phase lag of the feedback signal is controlled by a frequency regulation control loop. By continuously adjusting the phase lag of the feedback signal, the frequency of switching is maintained at a regulated value.

United States Patent Weischedel et al.

[451 May 23, 1972 [54] SELF-OSCILLATWG CONSTANT FREQUENCY SWITCHINGREGULATOR WITH PHASE CONTROL OF VOLTAGE REGULATION LOOP [72] Inventors:Herbert Rudolf Weischedel, Rockaway; George Raymond Westerman, Denville,

both of N .J

[73] Assignee: Bell Telephone Laboratories, Incorporated,

Murray Hill, NJ.

[22] Filed: Dec. 21, 1970 21 App1.No.: 100,233

1,438,211 1968 Germany ..323/DIG. 1

Primary Examiner-Gerald Goldberg AttorneyR. J. Guenther and E. W. Adams,Jr.

57 ABSTRACT A self-oscillating switching mode regulator is frequencyregulated by controlling the phase of the voltage control feedback [52]U.S. C1 323/l7, 321/2, 323/22 T, signal The phase lag of the feedbackSignal is controlled by a 323/38 323/DIG' 1 frequency regulation controlloop. By continuously adjusting [51 1 Int. Cl. ..G05f 1/56 the phase gof the feedback Signal, the frequency of [58] Field of Search.. ..321/2;323/17, 22 T, 22 SC, switching is maintained at a regulated va]ue323/38, DIG. l

6 Clains, 3 Drawing Figures Q3l0 37h 375 303 320 I a i;

F f 3 *4 345 347 I A k l 330 2L4 331 346L 348 r Patented May 23, 19723,665,291

2 Sheets-Sheet 1 FIG.

PRIOR ART lol @fino mos I03;

-|n i I05 10? I02 I09 I04 VOLTAGE ERROR DETECTOR FIG. 2

A W (20! fi2lo 225 206 20:?

X215 205 207 -2oa T SIGNAL W217 VOLTAGE ,209 PHASE ERROR CONTROLDETECTOR F REQUE NCY TO VOLTAGE CONVERTER H R. WE/SCHEOEL e. R.WESTL'RMAN A T TORNF V BACKGROUND OF THE INVENTION 7 This inventionrelates to switching mode voltage regulators. It is specificallyconcerned with the self-oscillating type switching regulator and relatesmore particularly to the regulation of the frequency of operation of theswitching regulator.

Switching mode regulators operate by transmitting pulses of energy froma source of continuous energy to an output terminal via a switchingdevice. The voltage level appearing at the output terminal is regulatedby comparing it to a reference signal. An error signal is generated bythis comparison and utilized to control the switching devicetransmitting the pulses of energy.

Switching mode regulators may be driven or self oscillating. The drivenswitching regulator transmits the pulses of energy at a fixed frequency.This fixed frequency is controlled by a discrete frequency source. Thedriven switching regulator switches at a constant frequency, but itsresponse to changes in the output voltagelevel may be delayed sincethere is a loss of regulation control during a portion of each switchingcycle.

The self-oscillating or-free running switching mode regulator inherentlycounteracts excursions of the output voltage beyond specified levels. Anadvantage of the self-oscillating switching regulator is its circuitsimplicity as compared with the driven switching regulator. A typicalself-oscillating switching mode voltage regulator shown in FIG. 1 has aseries switching transistor 110 inserted between an input terminal 101,to which power is applied, and an output terminal 103, to which a loadis connected. The series switching transistor 110 is controlled so thatit transmits energy whenever the voltage at terminal 103 drops below aspecified level. The transmission of energy through the transistor 1 10is inhibited when the voltage at the output terminal 103 rises aboveanother specified level.

The control circuitry utilized to control the switching of the switchingtransistor 110 includes a potentiometer 108 shunted across the outputterminals 103 and 104. A voltage proportionalto the voltage across theoutput terminals 103 and 104 is transmitted from the wiper arm of thepotentiometer 108 to a voltage error detector circuit109. The voltageerror detector circuit 109 comprises a source of reference voltage and acomparison circuit which generates a signal proportional to thedifference between the reference voltage and the voltage at the wiperarm of the potentiometer 108. The signal output of the voltage errordetector 109 is applied to an amplifier 1 l5 and from thence to the base111 of the switching transistor 110. This error signaldetermines theconductive state of the switching transistor 1 10.

In operation the output voltage of the regulator increases until theerror voltage output of detector 109 is sufiicient to bias the switchingtransistor 110 non-conducting.

During the nonconducting period of transistor 110 the load current issupplied, via the flyback diode 105, the inductor I06 and capacitor 107,to the output load. As the current in inductor 106 decays and capacitor107 discharges, the voltage across the output terminals 103 and 104begins to decrease. As the output voltage decreases, the error signaloutput of the voltage error detector 109 changes and when it crosses aspecified threshold the switching transistor 110 is biased intoconduction again. While this regulator circuit arrangement is fairlysimple and reliable, its frequency of operation is not constant. Forexample, the switching frequency responds to changes in the input sourcevoltage coupled to terminals 101 and 102 and to changes in the outputload impedance coupled to output terminals 103 and 104. In addition, thefrequency of operation may be responsive to entrainment of the switchingfrequency to some outside frequency source coupled to the regulator orby periodic signals which may be reflected from the output loadconnected to output-terminals 103 and 104.

It is therefore an object of the invention to regulate the frequency ofa self-oscillating switching regulator.

It is another object of the invention to control the phase angle of thevoltage control feedback signal in a switching regulator-in response tovariations in the switching frequency.

SUMMARY OF THE INVENTION The above objects are achieved by controllingthe reactance of the voltage control feedback circuit of a switchingregulator in response to its switching frequency. By varying thereactance of the feedback circuit, the phase angle of the voltagecontrol feedback signal is altered thereby controllably altering theswitching frequency of the regulator. The phase angle of the feedbacksignal is controllably varied in response to a frequency-to-voltageconverter whose voltage output is utilized to vary the reactance of thefeedback circuit.

BRIEF DESCRIPTION OF THE DRAWINGS A more comprehensive understanding ofthe invention may be acquired by reference to the following detaileddescription and drawings of illustrative embodiments of the invention,wherein:

FIG. 1 is a diagram of a typical switching mode regulator existing inthe prior art which is described hereinabove;

FIG. 2 is a diagram of a switching mode regulator which is frequencyregulated according to the principles of the invention; and

FIG. 3 is a schematic diagram of a switching regulator with a frequencyregulation feedback arrangement according to the principles of theinvention.

DETAILED DESCRIPTION The switching regulator, disclosed in FIG. 2,operates in substantially the same manner as does the switchingregulator described above and disclosed in FIG. 1. Energy from an inputvoltage source coupled to the input terminals 201 and 202 isintermittently transmitted by the switching transistor 210 to a loadconnected to the output terminals 203 and 204. The conduction periods ofthe switching transistor 210 are controlled in response to the voltageerror detector 209. The voltage error detector 209 monitors the outputvoltage, via the potentiometer 208, and applies appropriate switchingsignals, via the signal phase control 217 and amplifier 215, to theswitching transistor 210. During the nonconductive periods of thetransistor 210, energy is supplied to the load via the flyback diode205, the inductor 206, and the capacitor 207.

The frequency at which the switching transistor 210 switches isresponsive to changes in the input voltage and the output load. Thechanges which may occur in these parameters alter the load currentflowing through the switching transistor 210 and, in at least oneaspect, alter the storage time of transistor 210 hence changing itsswitching frequency. Other factors which may adversely affect theswitching frequency of transistor 210 include outside signal sources andperiodic signal reflections at the output terminals 203 and 204.

The switching regulator includes a frequency-tovoltage converter 216which is coupled to node 225 in order to monitor the switching frequencyof the switching transistor 210. The converter 216 generates a voltagedirectly proportional to this switching frequency and compares it to areference voltage generated internally by the switching regulator. Theconverter 216 derives a frequency error signal from this comparison andapplies this error signal to the signal phase control 217 in the voltagefeedback circuit.

The signal phase control 217 controls the relative phase of the voltagefeedback signal in the voltage feedback circuit. The control of thephase of the feedback signal directly compensates for variations in thestorage time of the switching transistor due to changes in the loadcurrent. For example, if the load current traversing transistor 210decreases, the switching frequency increases. In response to thisincrease, the frequency-to-voltage converter generates a frequency errorsignal which, applied to the signal phase control 217, retards the phaseof the feedback signal in the voltage feedback circuit. This phaseretardation reduces the natural frequency of the voltage feedbackcircuit and reduces the switching frequency of the switching transistor210 to its regulated value. The converse frequency regulation occurs ifthe load current increases.

The voltage regulator schematic disclosed in FIG. 3 cmbodies theprinciples and the features of the switching regulator shown in blockdiagram form in FIG. 2. A positive source whose voltage is to beregulated may be coupled to the input terminals 301 and 302. The load towhich the regulated voltage is to be applied may be coupled to theoutput terminals 303 and 304. When the input voltage is initiallyapplied to input terminals 301 and 302, the current through the baseemitter junctions of the transistors 310 and 320 and the biasingresistors 371 and 372 is sufficient to drive these two compoundconnected transistors into saturation.

With transistors 310 and 320 conducting, a load current flows from theinput terminal 301 through the collectoremitter path of transistor 310and the inductor 306 to the output terminal 303. This current energizesa load coupled across the output terminals 303 and 304 and causes avoltage drop thereacross. This output voltage is monitored by thevoltage error detector circuit 309. The error detector 309 is connectedto a potentiometer 365 which is shunted across the output tenninals 303and 304. This error detector circuit 309 comprises a transistor 360whose base electrode 361 is connected to the wiper ann of thepotentiometer 365. The voltage reference breakdown diode 364 establishesthe emitter voltage of the transistor 360. Hencethe conductivity oftransistor 360 is directly proportional to deviations of the outputvoltage of the regulator from its regulated value.

After conduction has been initiated in the transistor 310, the outputvoltage increases in magnitude. The increase in this voltage is detectedat the base electrode 361 of transistor 360, which is connected to thepotentiometer 365. The transistor 360 amplifies this voltage increaseand applies it, via the voltage feedback lead 373, to the base electrode331 of the transistor 330. The collector-emitter path of transistor 330shunts the emitter base paths of transistors 310 and 320.

As the output voltage increases in magnitude, the increased voltageapplied, via the potentiometer 365, to the base 361 of transistor 360biases it into a more highly conductive condition. As transistor 360becomes more conductive, its collector voltage decreases in value. Asthe collector voltage drops, it passes a threshold at which thetransistor 330 is biased into a conducting condition. With transistor330 conducting the emitter-base current which normally traversestransistors 310 and 320 is diverted through the conductive path oftransistor 330. Since the bias currents are removed from transistors 310and 320, these transistors turn 01f and no longer conduct current frominput terminal 301 to the output terminal 303. The output load currentis now supplied, via the ilyback diode 305 due to the energy stored inthe inductor 306 and capacitor 307.

The load current furnished by the stored energy in the inductor 306 andthe capacitor 307 begins to decay and the voltage drop across the loadconnected across terminals 303 and 304 decreases in magnitude. As thevoltage decreases, the voltage applied to the base electrode 361 of thedetector 309 decreases in magnitude, reducing the conductivity oftransistor 360. The collector voltage of transistor 360 consequentlyincreases. This increased collector voltage is applied, via the feedbacklead 373, to the base 331 and biases the transistor 330 into anonconducting condition. With transistor 330 nonconducting, the basecurrent through the base-emitter junction of transistor 310 andtransistor 320 is sufiicient to again initiate conduction in thesetransistors. The transistors3l0 and 320 become saturated in the samemanner as described above and the regulation cycle repeats itself.

As described above, the switching frequency of the regulator may vary inresponse to a change in any one of many parameters. Variables whichinduce frequency changes may involve changes in the input voltage,variations in the output load and changes in the load current. Theswitching frequency of the regulator is continuously monitored by thefrequencyto-voltage converter 316. The frequency-to-voltage converter316 has two terminals 377 and 378 which are connected across theinductor 306. Each time the switching transistor 310 is biased into anonconducting condition, a reverse voltage is induced in the inductor306. This reverse voltage biases the transistor 340 into a conductingcondition. The conduct ing transistor 340 transmits the regulatedvoltage appearing at the output terminal 303, via the capacitor 344 andthe diode 345, to the integrating capacitor 346. The two capacitors 344and 346 in combination with the diode 345 comprise a pulse countercircuit which counts the voltage reversals of the inductor 306. Thesevoltage reversals are directly proportional to the switching frequencyof the regulator. The charge on capacitor 346 discharges via theresistors 347 and 348 to ground. The frequency at which the transistor340 is biased into conduction determines the average voltage across thecapacitor 346.

The voltage feedback loop includes a signal phase control circuit 317which comprises a series connected combination of a transistor 350 andcapacitor 355. This series combination is shunted across thecollector-emitter junction of the transistor 360. The voltage across thecapacitor 346 is connected, via the voltage divider comprising theresistors 347 and 348, to the base electrode 351 of transistor 350. Theemitter voltage of transistor 350 is the reference voltage establishedby the breakdown diode 364. Hence the impedance of the transistor 350 isdirectly responsive to the deviation of the switching frequency from theregulated frequency. The value of the regulated frequency is determinedby the magnitude of the reference voltage.

It is readily apparent from the foregoing that as the impedance oftransistor 350 is adjusted, the relative effect of the capacitance ofcapacitor 355 on the voltage control feedback circuit is changed withrespect to frequency. If, for example, the frequency of the regulatorincreases, the frequency at which the transistor 340 is biased intoconduction increases. Hence in a given period of time, the number ofpulses counted by and stored on the capacitor 346 is increased,increasing the average voltage level thereon. This increased voltagelevel on the capacitor 346 biases the transistor 350 into a more highlyconductive condition and hence increases its conductivity. Hence therelative capacitance value respective to the total impedance of theparallel impedance, including transistors 350 and 360, increases. Thisadded capacitance introduces an added phase lag into the voltagefeedback signal applied, via lead 373, to the base 331 of the transistor330. This increased phase lag reduces the switching frequency of theregulator to its regulated value. A corresponding decrease in the phaselag occurs if the switching frequency decreases. This decrease in thephase lag acts to increase the switching frequency to its regulatedvalue.

It is apparent that the circuit can be modified to provide anindependent reference voltage to permit frequency adjust ment. Manyother modifications will be apparent to those skilled in the art withinthe scope of the invention.

What is claimed is:

l. A self-oscillating switching regulator to derive a regulated voltagefrom an unregulated voltage source comprising an input and an output,

a switching device coupling said input and output,

a voltage regulation feedback circuit to controlsaid switching deviceincluding an amplifier device responsive to the voltage at said output,said voltage regulation circuit further including means to control thephase of signals in the voltage regulation circuit,

a frequencyto-voltage converter responsive to the switching frequency ofsaid switching device,

said means to control the phase of signals including means to vary thereactance of said voltage feedback circuit comprising a reactive deviceand a variable impedance device connected in series, said seriesconnection shunting said amplifier device, and

said variable impedance device coupled to and responsive to saidfrequency-to-voltage converter.

2. A self-oscillating switching regulator as defined in claim 1 whereinsaid variable impedance device comprises a second amplifier deviceconnected in series with said reactive device, and

the conductivity of said second amplifier device being responsive tosaid frequency-to-voltage converter.

3. A self-oscillating switching regulator as defined in claim 2 whereinsaid frequency-to-voltage converter comprises a pulse differentiationcircuit and a diode pulse counter including a count storage capacitorwith a discharge path to drain said storage capacitor, and

said voltage across said storage capacitor being coupled to said secondamplifier device.

4, A self-oscillating switching regulator to supply a regulated outputvoltage from an unregulated voltage source comprising input and outputterminals,

a switching device interconnecting said input and output terminals andincluding a control electrode to control switching therein,

a voltage regulating feedback circuit including the conducting path ofan amplifying device having an input electrode coupled to and responsiveto the voltage at said output 7 terminal and coupled to said controlelectrode,

a frequency-to-voltage converter responsive to the frequency ofswitching of said switching device,

a signal phase control circuit in said feedback circuit including anenergy storage device and an electronically controllable impedanceresponsive to said converter connected in series, said series connectionshunting said amplifying device whereby the impedance and energy storagecharacteristics of said phase control circuit are altered in response tovariations in the frequency of switching of said switching device tocompensate for these frequency variations.

5. A self-oscillating switching regulator as defined in claim 4 whereintheconducting path of said amplifying device included in said voltageregulating feedback circuit comprises the collector-emitter path of afirst transistor,

said phase control circuit comprises a second transistor and a capacitorconnected in series with the collector-emitter path of said secondtransistor, and

said phase control circuit and said first transistor being connected inparallel.

6. A self-oscillating switching regulator as defined in claim 5 whereinsaid frequency-to-voltage converter includes means to integrate theoutput of said switching regulator, and

means to utilize said integrated output to control said phase controlcircuit including a source of reference voltage.

1. A self-oscillating switching regulator to derive a regulated voltagefrom an unregulated voltage source comprising an input and an output, aswitching device coupling said input and output, a voltage regulationfeedback circuit to control said switching device including an amplifierdevice responsive to the voltage at said output, said voltage regulationcircuit further including means to control the phase of signals in thevoltage regulation circuit, a frequency-to-voltage converter responsiveto the switching frequency of said switching device, said means tocontrol the phase of signals including means to vary the reactance ofsaid voltage feedback circuit comprising a reactive device and avariable impedance device connected in series, said series connectionshunting said amplifier device, and said variable impedance devicecoupled to and responsive to said frequency-to-voltage converter.
 2. Aself-oscillating switching regulator as defined in claim 1 wherein saidvariable impedance device comprises a second amplifier device connectedin series with said reactive device, and the conductivity of said secondamplifier device being responsive to said frequency-to-voltageconverter.
 3. A self-oscillating switching regulator as defined in claim2 wherein said frequency-to-voltage converter comprises a pulsedifferentiation circuit and a diode pulse counter including a countstorage capacitor with a discharge path to drain said storage capacitor,and said voltage across said storage capacitor being coupled to saidsecond amplifier device.
 4. A self-oscillating switching regulator tosupply a regulated output voltage from an unregulated voltage sourcecomprising input and output terminals, a switching deviceinterconnecting said input and output terminals and including a controlelectrode to control switching therein, a voltage regulating feedbackcircuit including the conducting path of an amplifying device having aninput electrode coupled to and responsive to the voltage at said outputterminal and coupled to said control electrode, a frequency-to-voltageconverter responsive to the frequency of switching of said switchingdevice, a signal phase control circuit in said feedback circuitincluding an energy storage device and an electronically controllableimpedance responsive to said converter connected in series, said seriesconnection shunting said amplifying device whereby the impedance andenergy storage characteristics of said phase control circuit are alteredin response to variations in the frequency of switching of saidswitching device to compensate for these frequency variations.
 5. Aself-oscillating switching regulator as defined in claim 4 wherein theconducting path of said amplifying device included in said voltageregulating feedback circuit comprises the collector-emitter path of afirst transistor, said phase control circuit comprises a secondtransistor and a capacitor connected in series with thecollector-emitter path of said second transistor, and said phase controlcircuit and said first transistor being connected in parallel.
 6. Aself-Oscillating switching regulator as defined in claim 5 wherein saidfrequency-to-voltage converter includes means to integrate the output ofsaid switching regulator, and means to utilize said integrated output tocontrol said phase control circuit including a source of referencevoltage.